Valve-controlled sealed lead-acid batteries have been widely used due to its ability to have a smooth, low cost, use and maintenance convenience, etc. VRLA batteries will still be the main force of backup power supplies and energy storage equipment in the fields of communications, electricity, rail transit.Be
Although the valve-free sealed lead-acid battery is known as "maintenance", the market is now many, the fish dragon is mixed, and the quality is uneven, and in actual use, due to the deterioration of the battery itself, the capacity of the battery is constantly declining , Especially in actual use, usually a plurality of batteries are used in series, which makes the performance degradation of a battery that can drag the performance of the entire set of batteries, so that the battery pack does not meet the design capacity, once the power outage, the accident occurred Sexual increases, so daily for the monitoring and maintenance of the battery pack is essential, so that the battery failure will bring losses to electric customers. This article makes a comprehensive introduction and analysis on the development and status of monitoring technology of VRLA batteries.
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Traditional battery monitoring method
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For a long time, the maintenance unit of the battery is manually maintained, the most common is the following ways: 1.1. Checlature discharge This method is to most accurately know how battery capacity. The specific operation is to disengage the battery pack of the floating state, and then discharge at a speed of 0.1c of the battery nominal capacity (i.e., the battery of 100ah is discharged at 10A), and records the battery to reach the predetermined termination voltage. Determine the actual capacity of the battery. The biggest advantage of this method is accurate, but the disadvantage is also obvious: this method needs to operate, there is a risk; if it is necessary to leave the load, there is no power supply in the discharge, the system does not have a reserve power supply; Methods The capacity of the worst battery monomer in the battery pack is tested, and the capacity of other battery cells still has no mastery; it also has certain damage to the battery capacity itself, so the battery cannot be checked to discharge the battery, general purpose The frequency of this test is 1-2 times a year, and the process of battery deterioration is often happened in a few weeks, so that the battery in the two test intervals is still unknown, the accident hidden danger still exists.
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1.2. Online or manual monitoring battery voltage
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This is the most commonly used method for monitoring the state of the battery for a long time. However, it can be seen from the figure below that in the floating state, the floating voltage of different batteries is almost consistent. By the discharge test can see the capacity abnormally, the battery will soon fall to the cutoff voltage, so that through this The method of determining the capacity of the battery is invalid.
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1.3. Manual measuring battery internal resistance
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This method is usually used in common with method 2 to discriminate the battery. That is, the maintenance personnel use the internal resistance to manually test the internal resistance of the battery cell. So far, although a large number of literatures indicate that the internal resistance and capacity status of the battery is not a clear mathematical correspondence, the recognized internal resistance in the industry is related to the change in capacity. In Figure 2, the yellow trend line shows the internal resistance of the battery during October to November, because various reasons have risen sharply, it can be judged that the state of the battery has been severely deteriorated, and the discharge of the battery is confirmed that the battery has failed.
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However, the shortcomings of this method are also obvious: the state of the battery cannot be monitored in real time; the time spent is long, the cost is high; some battery packs are not facilitated by the space; each test due to different data due to personnel and instruments There will be a big difference. This test method is no longer adapted to the current demand for battery monitoring systems, and it is instead of the online internal resistance monitoring. Let's take a detailed introduction to this monitoring method.
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2. Online battery internal resistance monitor
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This monitoring method is divided into centralized and distributed from the system architecture.
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2.1 Centralized online battery internal resistance system
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The centralized monitoring system refers to the test of a group or even multiple sets of batteries to test on the same device. Figure 3 is an example of a centralized monitoring system.
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Centralized monitoring system Test battery internal resistance uses an AC injection method, that is, a certain frequency and amplitude communication (substantially sinusoidal) signal is injected into both ends of the battery in the device, and then detected and detected the same frequency on both ends of the battery. Voltage fluctuations can determine the internal resistance of the battery. AC injection method is also a method of detecting internal resistance in hand-held internal resistance instrument. The AC injection method does not need to take electricity from the battery, which will not affect the capacity and life of the battery itself. However, the current injection method is generally not too large (1A or less) to avoid the production of the power environment system *, such a small current caused by the battery voltage is very difficult to accurately test, and it is easy to accept the power environment system. Noise *, especially there is a lot of harmonics * on both ends of the UPS system *, how to filter out these * is a very challenging job. In the current concentrated equipment test internal resistance, most of the precision is not ideal, and the distributed acquisition module still has a gap. The centralized device is required to collect parameters of multiple battery cells, which requires a large number of cables from the device, and since the length of the battery is different, the lengths and traces of these connecting lines are inconsistent, thereby making centralized monitoring System construction and maintenance is more troublesome.
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Although centralized monitoring methods have various drawbacks, due to its low cost, there is still a considerable market in some cases that are not high for internal resistance precision requirements. Manufacturers of the production of centralized equipment include Emerson, Hangzhou Gaotong, and some smaller vendors.
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2.2 Distributed Online Battery Internal Removal Surmling System
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In relatively centralized monitoring, the battery parameter acquisition module of the distributed system corresponds to one or one, and the acquisition module is fixed to the battery surface by a guide or double-sided adhesive. Since each battery cell is configured, the connection line is short, so that this makes The on-site construction wiring is very simple.
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In a distributed monitoring system, the battery parameter acquisition module will receive the collected data to the field host on the serial bus, and then report to the center server on the field host, and the user can view the status parameters of the battery run through the client access server.
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The battery parameter acquisition module of the distributed system is smaller, and the signal cannot be generated inside. It is necessary to take electricity from the battery itself, so the method of testing internal resistance generally uses DC or AC discharge method, that is, taking the battery Specific frequency and amplitude DC (pulse) or AC (sinusoidal) current, then determine the internal resistance of the battery by testing the voltage fluctuations at both ends of the battery. Since there is more harmonic components contained in the pulse signal, it is more complicated for post-signal processing, and the communication discharge method is better from the accuracy of the internal resistance result accuracy. With the use of DC discharge law, Laim, Hua Plastic, etc., Hai Weichen Electronics and other companies use AC discharge method.
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3. Battery parameter acquisition module performance indicator
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Measuring the performance indicators of the module internal resistance test include the absolute accuracy of the test, the repeated test results, the statically losses of the module, and the dynamic loss of the module test, and the security performance of the module.
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3.1 absolute accuracy
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The absolute accuracy of the internal resistance measurement refers to the difference between the value of the internal resistance test of the sensor and the real internal resistance value. The results of the test should be closer to the true value, but this indicator has lacks the basis for judgment because the internal resistance value of the battery does not have a standard value. Even some people are not important, but the author seems to be an important indicator for measuring a performance of a module, because many battery install monitoring systems have been used for a while, it is difficult to test if the test is not accurate The initial internal resistance value (provided) is compared to determine the capacity state of the battery. Solving this problem is also very simple, you can simulate the battery internal resistance with a standard precision resistance, and then test the resistance of the resistor to determine the absolute accuracy of the acquisition module.
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3.2 Repeat of test results
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The repeating of the internal resistance test refers to the same battery monomer, under the same time and the same conditions, with the same acquisition module repeatedly measures the internal resistance value, the deviation range of the resulting result. It is to be pointed out that the conditions for measuring this indicator are not only when the battery is working offline, but also considers the consistency of the test results of the system when the battery has a large harmonic * when the battery is working online. Test Indicates that many manufacturers' acquisition modules are very discrete, and some modules do not work properly in the case of *.
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3.3 Module loss
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Loss consumes a dynamic loss of static losses and test parameters when the module does not test. Static loss is an important parameter in the case of battery offline, because distributed modules are taken from the battery itself, and if the static loss is too large, the consumption of the battery itself is also large. The dynamic loss is mainly the size of the current pulling current from the battery when the module is tested. The smaller the current, the smaller the impact of the battery, but the voltage fluctuations caused by too small current are also small, and the design of the signal detection circuit The corresponding improvement is thereby affected the accuracy of the final test results. The size of the existing module pull current in the market will not wait from hundreds of milliamps to several amps.
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3.4 Safety performance of the module
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The security performance of the module means whether the module does not affect the security of the system in the event of a fault. This requires the module to be physically separated from the battery during internal short circuit, and in the case where the battery is positive and negative, the module itself requires reverse protection to avoid reverse time modules. damage.
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4. Decision of battery capacity status
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For battery users, the most concerned parameters are still the current capacity state of the battery, often in the battery's health parameters (SOH). As we have a certain relationship between the internal resistance and capacity of the battery, there is no clear mathematical corresponding formula, so how to convert the internal resistance of the test into the health parameters of the battery is a big challenging work. Some companies have made some research in this regard, but also develop computing software, but from the results, they have not reached a very accurate level, and they can only play some reference roles. This work is still to continue to study in all aspects.
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5. Conclusion
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As a ring in the dynamic environment monitoring, the battery monitoring is gradually attached. Battery monitoring has developed rapidly in recent years, emerges in various new technologies and new products, of which the internal resistance of the battery is tested to monitor the capacity of the battery into mainstream. With the promotion of these new technologies and products, the maintenance of the battery will be transferred from artificial, disperse to automation and centralize.
Article from: http://www.brcpower.com/ Recommend: LiFePO4 Battery Manufacturer Energy storage battery Manufacturer Integrated machine energy storage battery series Manufacturer Lead lithium battery Manufacturer Outdoor Backup Battery Manufacturer Portable outdoor power supply Manufacturer Power battery Manufacturer Powerwall LiFePO4 Battery Manufacturer Battery rack Manufacturers Telecom LiFePO4 Battery Manufacturer Wall mounted battery storage Manufacturer China Lifepo4 Battery
